1. Field of the Invention
The present invention relates to lead-free free-cutting copper alloys.
2. Prior Art
Among the copper alloys with a good machinability are bronze alloys such as that having the JIS designation H5111 BC6 and brass alloys such as those having the JIS designations H3250-C3604 and C3771. These alloys are enhanced in machinability by the addition of 1.0 to 6.0 percent, by weight, of lead, and provide an industrially satisfactory machinability. Because of their excellent machinability, those lead-contained copper alloys have been an important basic material for a variety of articles such as city water faucets, water supply/drainage metal fittings and valves.
However, the application of those lead-mixed alloys has been greatly limited in recent years, because lead contained therein is an environmental pollutant harmful to humans. That is, the lead-contained alloys pose a threat to human health and environmental hygiene because lead is contained in metallic vapor that is generated in the steps of processing those alloys at high temperatures, such as in melting and casting operations. There is also a concern that lead contained in water system metal fittings, valves, and other components made of those alloys will dissolve out into drinking water.
For these reasons, the United States and other advanced countries have been moving to tighten the standards for lead-contained copper alloys, drastically limiting the permissible level of lead in copper alloys in recent years. In Japan, too, the use of lead-contained alloys has been increasingly restricted, and there has been a growing call for development of free-cutting copper alloys with a low lead content.
It is an object of the present invention to provide a lead-free copper alloy which does not contain the machinability-improving element lead, yet is quite excellent in machinability and can be used as safe substitute for the conventional free cutting (easy-to-cut) copper alloy that has a high lead content, with concomitant environmental hygienic problems. The lead-free copper alloy of the present invention also permits recycling of chips without problems. Thus, the present invention presents a timely answer to the mounting call for restriction of lead-containing products.
It is an another object of the present invention to provide a lead-free copper alloy that has high corrosion resistance as well as excellent machinability, and is suitable as basic material for cutting works, forgings, castings, and other applications, thus having a very high practical value. The cutting works, forgings, castings, and other applications include city water faucets, water supply/drainage metal fittings, valves, stems, hot water supply pipe fittings, shaft and heat exchanger parts.
It is yet another object of the present invention to provide a lead-free copper alloy with high strength and wear resistance as well as machinability. This lead-free copper alloy is suitable as basic material for the manufacture of cutting works, forgings, castings, and other uses requiring high strength and wear resistance such as, for example, bearings, bolts, nuts, bushes, gears, sewing machine parts, and hydraulic system parts. Hence, this embodiment of the present invention has a very high practical value.
It is a further object of the present invention to provide a lead-free copper alloy with excellent high-temperature oxidation resistance as well as machinability, which alloy is suitable as basic material for the manufacture of cutting works, forgings, castings, and other uses where high thermal oxidation resistance is essential, e.g., nozzles for kerosene oil and gas heaters, burner heads, and gas nozzles for hot-water dispensers. Hence, this embodiment of the present invention too has a very high practical value.
The objects of the present inventions are achieved by provision of the following copper alloys:
A lead-free free-cutting copper alloy with an excellent machinability, which is composed of 69 to 79 percent, by weight, of copper, more than 3.0 to 4.0 percent or less, by weight, of silicon, and the remaining percent, by weight, of zinc, wherein the percent by weight of copper and silicon in the copper alloy satisfy the relationship; 55xe2x89xa6Xxe2x88x923Yxe2x89xa670, wherein X is the percent, by weight, of copper, and Y is the percent, by weight, of silicon; and the copper alloy has a metal construction comprising multiple phases integrated to form a composite phase, wherein the composite phase is an xcex1 phase matrix having a total phase area comprising not more than 5% of a xcex2 phase, and 5-70% of the total phase area is provided by at least one phase selected from the group consisting of a xcex3 phase, a xcexa phase, and a xcexc phase. For purpose of simplicity, this copper alloy will be hereinafter called the xe2x80x9cfirst invention alloyxe2x80x9d.
Lead does not form a solid solution in the matrix but instead disperses in a granular form to improve the machinability of an alloy. Silicon enhances the easy-to-cut property of an alloy by producing a gamma phase (in some cases, a kappa phase) in the structure of metal. That way, both act to improve alloy machinability, though they are quite different in their respective contributions to the properties of the alloy. On the basis of that recognition, silicon is added to the first invention alloy in place of lead so as to bring about a high level of machinability meeting industrial requirements. That is, the first invention alloy is improved in machinability through formation of a gamma phase with the addition of silicon.
The addition of less than 2.0 percent, by weight, of silicon cannot form a gamma phase sufficient to provide industrially satisfactory machinability. With increases above 2.0 weight-percent in the addition of silicon, the machinability improves. But with the addition of more than 4.0 percent, by weight, of silicon, the machinability will not improve proportionally. A problem is, however, that silicon has a high melting point and a low specific gravity and is also liable to oxidize. If silicon alone is fed in a simple substance into a furnace in an alloy melting step, silicon will float on the molten metal and be oxidized into oxides of silicon (or silicon oxide), hampering production of a silicon-containing copper alloy. In making an ingot of silicon-containing copper alloy, therefore, silicon is usually added in the form of a Cuxe2x80x94Si alloy, which boosts the production cost. In the light of the cost of making the alloy, too, it is not desirable to add silicon in a quantity exceeding the saturation point where machinability improvement levels off, i.e., 4.0 percent by weight. Experimentation has shown that when silicon is added in an amount of more than 3.0 percent and up to and including 4.0 percent, by weight, it is desirable to hold the content of copper to 69 to 79 percent, by weight, in consideration of its relation to the content of zinc in order to maintain the intrinsic properties of the Cuxe2x80x94Zn alloy. For this reason, the first invention alloy is composed of 69 to 79 percent, by weight, of copper and more than 3.0 percent and up to and including 4.0 percent, by weight, of silicon. It is stressed that the range of silicon content included, by weight, in the composition of the first invention alloy excludes 3 percent, by weight, of silicon. The addition of silicon, as specified above, improves not only the machinability but also the flow of the molten metal in casting, strength, wear resistance, resistance to stress corrosion cracking, high-temperature oxidation resistance. Also, the ductility and dezincification resistance will be improved to some extent.
A lead-free free-cutting copper alloy, also with an excellent machinability, which is composed of 69 to 79 percent, by weight, of copper; 2.0 to 4.0 percent, by weight, of silicon; at least one element selected from among 0.02 to 0.4 percent, by weight, of bismuth, 0.02 to 0.4 percent, by weight, of tellurium, and 0.02 to 0.4 percent, by weight, of selenium; and the remaining percent, by weight, of zinc, wherein the percent by weight of copper and silicon in the copper alloy satisfy the relationship; 55xe2x89xa6Xxe2x88x923Yxe2x89xa670, wherein X is the percent, by weight, of copper, and Y is the percent, by weight, of silicon; and the copper alloy has a metal construction comprising multiple phases integrated to form a composite phase, wherein the composite phase is an xcex1 phase matrix having a total phase area comprising not more than 5% of a xcex2 phase, and 5-70% of the total phase area is provided by at least one phase selected from the group consisting of a xcex3 phase, a xcexa phase, and a xcexc phase. This second copper alloy will be hereinafter called the xe2x80x9csecond invention alloy.xe2x80x9d
That is, the second invention alloy is composed of the first invention alloy and at least one element selected from among 0.02 to 0.4 percent, by weight, of bismuth, 0.02 to 0.4 percent, by weight, of tellurium, and 0.02 to 0.4 percent, by weight, of selenium.
Bismuth, tellurium, and selenium, like lead, do not form a solid solution in the matrix but disperse in granular form to enhance machinability through a mechanism different from that of silicon. Hence, the addition of those elements along with silicon could further improve the machinability beyond the level obtained by the addition of silicon alone. From this finding, the second invention alloy is provided in which at least one element selected from among bismuth, tellurium, and selenium is mixed to further improve the machinability obtained by the first invention alloy. The addition of bismuth, tellurium, or selenium in addition to silicon produces a high machinability such that complicated forms can be freely cut at a high speed. But no improvement in machinability can be realized from the addition of bismuth, tellurium, or selenium in an amount less than 0.02 percent, by weight. However, those elements are expensive as compared with copper. Even if the addition exceeds 0.4 percent by weight, the proportional improvement in machinability is so small that the addition beyond that does not pay economically. What is more, if the addition is more than 0.4 percent by weight, the alloy will deteriorate in hot workability such as forgeability and cold workability such as ductility. While there might be a concern that heavy metals like bismuth would cause problems similar to those of lead, addition of a very small amount of less than 0.4 percent by weight is negligible and would present no particular problems. Based upon these considerations, the second invention alloy is prepared with the addition of bismuth, tellurium, or selenium kept to 0.02 to 0.4 percent by weight. The addition of those elements, which positively affect the machinability of the copper alloy though a mechanism different from that of silicon, as mentioned above, would not affect the proper contents of copper and silicon. On this ground, the contents of copper and silicon in the second invention alloy are set at the same level as those in the first invention alloy.
A lead-free free-cutting copper alloy that also has excellent machinability which is composed of 70 to 80 percent, by weight, of copper; 1.8 to 3.5 percent, by weight, of silicon; at least one element selected from among 0.3 to 3.5 percent, by weight, of tin, and 0.02 to 0.25 percent, by weight, of phosphorus; and the remaining percent, by weight, of zinc, wherein the percent by weight of copper, silicon, tin and phosphorus in the copper alloy satisfy the relationship; 55xe2x89xa6Xxe2x88x923Y+aZ+bWxe2x89xa670, wherein X is the percent, by weight, of copper, Y is the percent, by weight, of silicon, Z is the percent, by weight, of tin, W is the percent, by weight, of phosphorus, a is xe2x88x920.5, and b is xe2x88x923; and the copper alloy has a metal construction comprising multiple phases integrated to form a composite phase, wherein the composite phase is an xcex1 phase matrix having a total phase area comprising not more than 5% of a xcex2 phase, and 5-70% of the total phase area is provided by at least one phase selected from the group consisting of a xcex3 phase, a xcexa phase, and a xcexc phase. This third copper alloy will be hereinafter called the xe2x80x9cthird invention alloy.xe2x80x9d
Tin works the same way as silicon. That is, if tin is added to the Cuxe2x80x94Zn alloy, a gamma phase will be formed and the machinability of the Cuxe2x80x94Zn alloy will be improved. For example, the addition of tin in an amount of 1.8 to 4.0 percent by weight would bring about a high machinability in the Cuxe2x80x94Zn alloy containing 58 to 70 percent, by weight, of copper; even if silicon is not added. Therefore, the addition of tin to the Cuxe2x80x94Sixe2x80x94Zn alloy can facilitate the formation of a gamma phase and further improve the machinability of the Cuxe2x80x94Sixe2x80x94Zn alloy. The gamma phase is formed with the addition of tin in an amount of 1.0 or more percent by weight, and gamma phase formation reaches the saturation point at 3.5 percent, by weight, of tin. If tin exceeds 3.5 percent by weight, the ductility will drop instead. With the addition of tin in amounts less than 1.0 percent by weight, on the other hand, no gamma phase will be formed. If the addition is 0.3 percent or more by weight, then tin will be effective in uniformly dispersing the gamma phase formed by silicon. Machinability is improved through that effect of dispersing the gamma phase. In other words, the addition of tin in amounts of not less than 0.3 percent by weight improves the machinability of the alloy.
As for phosphorus, it has no property of forming the gamma phase as in the case of tin. However, phosphorus works to uniformly disperse and distribute the gamma phase formed as a result of the addition of silicon alone or with tin. In that way, improvement in machinability through gamma phase formation is further enhanced. In addition to dispersing the gamma phase, phosphorus helps to refine the crystal grains in the alpha phase in the matrix, improving hot workability and also strength and resistance to stress corrosion cracking. Furthermore, phosphorus substantially increases the flow of molten metal in casting. To produce such results, phosphorus will have to be added in an amount not smaller than 0.02 percent by weight. But if the addition exceeds 0.25 percent by weight, no proportional effect is obtained. Instead, there will be a decrease in hot forging properties and in extrudability.
In consideration of those observations, the third invention alloy is improved in machinability by adding to the Cuxe2x80x94Sixe2x80x94Zn alloy at least one element selected from among 0.3 to 3.5 percent, by weight, of tin, and 0.02 to 0.25 percent, by weight, of phosphorus.
Meanwhile, tin and phosphorus serve to improve the machinability by forming a gamma phase or dispersing that phase, and work closely with silicon in promoting the improvement in machinability through the gamma phase. In the third invention alloy mixed with silicon along with tin or phosphorus, therefore, silicon does not work alone. Machinability is improved not only by the silicon, but by tin or phosphorus, and thus the required addition of silicon is smaller than that in the second invention alloy in which the machinability is enhanced by adding bismuth, tellurium, or selenium. That is, those elements bismuth, tellurium, and selenium contribute to improving the machinability, not by acting on the gamma phase but by dispersing in the form of grains in the matrix. Even if the addition of silicon is less than 2.0 percent by weight, silicon along with tin or phosphorus will be able to enhance the machinability to an industrially satisfactory level as long as the percentage of silicon is 1.8 or more percent by weight. But even if the addition of silicon is not larger than 4.0 percent by weight, the effect of silicon in improving machinability is saturated and is not promoted any further in the cases where tin or phosphorus is added, when the silicon content exceeds 3.5 percent by weight. For this reason, the addition of silicon is set at 1.8 to 3.5 percent by weight in the third invention alloy. Also, in consideration of the added amount of silicon and also the addition of tin or phosphorus, the content range of copper in this third invention alloy is slightly raised from the level in the second invention alloy and is set at 70 to 80 percent by weight as preferred content of copper.
A lead-free free-cutting copper alloy also with an excellent easy-to-cut (i.e., machinability) feature which is composed of 70 to 80 percent, by weight, of copper; 1.8 to 3.5 percent, by weight, of silicon; at least one element selected from among 0.3 to 3.5 percent, by weight, of tin and 0.02 to 0.25 percent, by weight, of phosphorus; at least one element selected from among 0.02 to 0.4 percent, by weight, of bismuth, 0.02 to 0.4 percent, by weight, of tellurium, and 0.02 to 0.4 percent, by weight, of selenium; and the remaining percent, by weight, of zinc, wherein the percent by weight of copper, silicon, tin and phosphorus in the copper alloy satisfy the relationship; 55xe2x89xa6Xxe2x88x923Y+aZ+bWxe2x89xa670, wherein X is the percent, by weight, of copper, Y is the percent, by weight, of silicon, Z is the percent, by weight, of tin, W is the percent, by weight, of phosphorus, a is xe2x88x920.5, and b is xe2x88x923; and the copper alloy has a metal construction comprising multiple phases integrated to form a composite phase, wherein the composite phase is an xcex1 phase matrix having a total phase area comprising not more than 5% of a xcex2 phase, and 5-70% of the total phase area is provided by at least one phase selected from the group consisting of a xcex3 phase, a xcexa phase, and a xcexc phase. This fourth copper alloy will be hereinafter called the xe2x80x9cfourth invention alloy.xe2x80x9d
The fourth invention alloy thus contains at least one element selected from among 0.02 to 0.4 percent, by weight, of bismuth, 0.02 to 0.4 percent, by weight, of tellurium, and 0.02 to 0.4 percent, by weight, of selenium, in addition to the components in the third invention alloy. The grounds for adding those additional elements and setting the amounts to be added are the same as given for the second invention alloy.
A lead-free free-cutting copper alloy having excellent machinability and exhibiting a high degree of corrosion resistance, which is composed of 69 to 79 percent, by weight, of copper; 2.0 to 4.0 percent, by weight, of silicon; at least one element selected from among 0.3 to 3.5 percent, by weight, of tin and 0.02 to 0.25 percent, by weight, of phosphorus, at least one element selected from among 0.02 to 0.15 percent, by weight, of antimony, and 0.02 to 0.15 percent, by weight, of arsenic, and the remaining percent, by weight, of zinc, wherein the percent by weight of copper, silicon, tin and phosphorus in the copper alloy satisfy the relationship; 55xe2x89xa6Xxe2x88x923Y+aZ+bWxe2x89xa670, wherein X is the percent, by weight, of copper, Y is the percent, by weight, of silicon, Z is the percent, by weight, of tin, W is the percent, by weight, of phosphorus, a is xe2x88x920.5, and b is xe2x88x923; and the copper alloy has a metal construction comprising multiple phases integrated to form a composite phase, wherein the composite phase is an xcex1 phase matrix having a total phase area comprising not more than 5% of a xcex2 phase, and 5-70% of the total phase area is provided by at least one phase selected from the group consisting of a xcex3 phase, a xcexa phase, and a xcexc phase. This fifth copper alloy will be hereinafter called the xe2x80x9cfifth invention alloy.xe2x80x9d
The fifth invention alloy thus contains at least one element selected from among 0.3 to 3.5 percent, by weight, of tin and 0.02 to 0.25 percent, by weight, of phosphorus, at least one element selected from among 0.02 to 0.15 percent, by weight, of antimony, and 0.02 to 0.15 percent, by weight, of arsenic, in addition to the first invention alloy.
Tin is effective in improving not only the machinability but also the corrosion resistance properties (dezincification resistance and erosion corrosion resistance) and forgeability of the alloy. In other words, tin improves the corrosion resistance in the alpha phase matrix and, by dispersing the gamma phase, the corrosion resistance, forgeability, and stress corrosion cracking resistance. The fifth invention alloy is thus improved in corrosion resistance by such property of tin and in machinability mainly by adding silicon. Therefore, the contents of silicon and copper in this alloy are set at the same as those in the first invention alloy. To raise the corrosion resistance and forgeability, on the other hand, tin would have to be added in an amount of at least 0.3 percent by weight. But even if the addition of tin exceeds 3.5 percent by weight, the corrosion resistance and forgeability will not improve in proportion to the added amount of tin. The addition of amounts of tin in excess of 3.5 percent by weight is, therefore, uneconomical.
As described above, phosphorus disperses the gamma phase uniformly and at the same time refines the crystal grains in the alpha phase in the matrix, thereby improving the machinability and also the corrosion resistance properties (dezincification resistance and erosion corrosion resistance), forgeability, stress corrosion cracking resistance, and mechanical strength. The fifth invention alloy is thus improved in corrosion resistance and other properties by such properties of phosphorus and in machinability mainly by adding silicon. The addition of phosphorus in a very small quantity; that is, 0.02 or more percent by weight can produce beneficial results. But the addition in an amount of more than 0.25 percent by weight would not produce proportional benefits, and instead would reduce hot forgeability and extrudability.
Just as with phosphorus, antimony and arsenic in a very small quantities xe2x88x920.02 or more percent by weightxe2x80x94are effective in improving the dezincification resistance and other properties. But their addition in amounts exceeding 0.15 percent by weight would not produce results in proportion to the quantity mixed. Instead, it would lower the hot forgeability and extrudability, as would phosphorus applied in excessive amounts.
Those observations indicate that the fifth invention alloy is improved in machinability and also corrosion resistance and other properties by adding at least one element selected from among tin and phosphorus, and by adding at least one element selected from among antimony and arsenic, in quantities within the aforesaid limits, in addition to the same quantities of copper and silicon as in the first invention copper alloy. In the fifth invention alloy, the additions of copper and silicon are set at 69 to 79 percent by weight and 2.0 to 4.0 percent by weight respectivelyxe2x80x94the same level as in the first invention alloy in which any other machinability improver than silicon is not addedxe2x80x94because tin and phosphorus work mainly as corrosion resistance improvers like antimony and arsenic.
A lead-free free-cutting copper alloy, also with excellent machinability and with high corrosion resistance, which is composed of 69 to 79 percent, by weight, of copper; 2.0 to 4.0 percent, by weight, of silicon; at least one element selected from among 0.3 to 3.5 percent, by weight, of tin and 0.02 to 0.25 percent, by weight, of phosphorus, at least one element selected from among 0.02 to 0.15 percent, by weight, of antimony, and 0.02 to 0.15 percent, by weight, of arsenic; at least one element selected from among 0.02 to 0.4 percent, by weight, of bismuth, 0.02 to 0.4 percent, by weight, of tellurium, and 0.02 to 0.4 percent, by weight, of selenium; and the remaining percent, by weight, of zinc, wherein the percent by weight of copper, silicon, tin and phosphorus in the copper alloy satisfy the relationship; 55xe2x89xa6Xxe2x88x923Y+aZ+bWxe2x89xa670, wherein X is the percent, by weight, of copper, Y is the percent, by weight, of silicon, Z is the percent, by weight, of tin, W is the percent, by weight, of phosphorus, a is xe2x88x920.5, and b is xe2x88x923; and the copper alloy has a metal construction comprising multiple phases integrated to form a composite phase, wherein the composite phase is an xcex1 phase matrix having a total phase area comprising not more than 5% of a xcex2 phase, and 5-70% of the total phase area is provided by at least one phase selected from the group consisting of a xcex3 phase, a xcexa phase, and a xcexc phase. This sixth copper alloy will be hereinafter called the xe2x80x9csixth invention alloy.xe2x80x9d
The sixth invention alloy thus contains at least one element selected from among 0.02 to 0.4 percent, by weight, of bismuth, 0.02 to 0.4 percent, by weight, of tellurium, and 0.02 to 0.4 percent, by weight, of selenium, in addition to the components in the fifth invention alloy. The machinability of the alloy is improved by adding silicon and at least one element selected from among bismuth, tellurium, and selenium as in the second invention alloy and the corrosion resistance and other properties are raised by using at least one element selected from among tin, phosphorus, antimony, and arsenic as in the fifth invention alloy. Therefore, the additions of copper, silicon, bismuth, tellurium, and selenium are set at the same levels as those in the second invention alloy, while the contents of tin, phosphorus, antimony, and arsenic are adjusted to the levels of the same elements in the fifth invention alloy.
A lead-free free-cutting copper alloy, also with excellent machinability and with excellent high strength features and high corrosion resistance, which is composed of 62 to 78 percent, by weight, of copper; 2.5 to 4.5 percent, by weight, of silicon; at least one element selected from among 0.3 to 3.0 percent, by weight, of tin and 0.02 to 0.25 percent, by weight, of phosphorus; and at least one element selected from among 0.7 to 3.5 percent, by weight, of manganese and 0.7 to 3.5 percent, by weight, of nickel; and the remaining percent, by weight, of zinc, wherein the percent by weight of copper, silicon, tin, phosphorus, manganese and nickel in the copper alloy satisfy the relationship; 55xe2x89xa6Xxe2x88x923Y+aZ+bW+cV+dUxe2x89xa670, wherein X is the percent, by weight, of copper, Y is the percent, by weight, of silicon, Z is the percent, by weight, of tin, W is the percent, by weight, of phosphorus, V is the percent, by weight, of manganese, U is the percent, by weight, of nickel, a is xe2x88x920.5, b is xe2x88x923, c is 2.5, d is 2.5, and the percent by weith of silicon, manganese and nickel satisfy the relationship; 0.7xe2x89xa6Y/(V+U)xe2x89xa66; and the copper alloy has a metal construction comprising multiple phases integrated to form a composite phase, wherein the composite phase is an xcex1 phase matrix having a total phase area comprising not more than 5% of a xcex2 phase, and 5-70% of the total phase area is provided by at least one phase selected from the group consisting of a xcex3 phase, a xcexa phase, and a xcexc phase. The seventh copper alloy will be hereinafter called the xe2x80x9cseventh invention alloy.xe2x80x9d
Manganese and nickel combine with silicon to form intermetallic compounds, which may be represented by the formulas MnxSiy or NixSiy, which intermetallic compounds are evenly precipitated in the matrix, thereby raising the wear resistance and strength of the alloy containing them. Thus the addition of manganese and/or nickel improves high strength features and wear resistance. Improved effects are exhibited when manganese and nickel are added in amounts not less than 0.7 percent by weight, respectively. But the saturation state is reached at 3.5 percent by weight, and even if the addition is increased beyond that, no proportional results will be obtained. The addition of silicon is set at 2.5 to 4.5 percent by weight to match the addition of manganese or nickel, taking into consideration the consumption to form intermetallic compounds with those elements.
It is also noted that tin and phosphorus help to reinforce the alpha phase in the matrix, thereby improving strength, wear resistance, and also machinability. Tin and phosphorus disperse the alpha and gamma phases, by which the strength, wear resistance, and machinability are improved. Tin in an amount of 0.3 or more percent by weight is effective in improving the strength and machinability. However, if the addition exceeds 3.0 percent by weight, ductility will decrease. For this reason, the addition of tin is set at 0.3 to 3.0 percent by weight, to raise the high strength features and wear resistance in the seventh invention alloy and also to enhance the machinability thereof. The addition of phosphorus disperses the gamma phase and at the same time refines the crystal grains in the alpha phase in the matrix, thereby improving hot workability as well as the strength and wear resistance. Furthermore, phosphorus is very effective in improving the flow of molten metal in casting. Such results will be produced when phosphorus is added in the range of 0.02 to 0.25 percent by weight. The content of copper is set at 62 to 78 percent by weight, in view of the addition of silicon and the bonding of silicon with manganese and nickel.
A lead-free free-cutting copper alloy, also with excellent machinability and with excellent high strength features as well as high wear resistance, comprises 62 to 78 percent, by weight, of copper; 2.5 to 4.5 percent, by weight, of silicon; at least one element selected from among 0.3 to 3.0 percent, by weight, of tin and 0.02 to 0.25 percent, by weight, of phosphorus; and at least one element selected from among 0.7 to 3.5 percent, by weight, of manganese and 0.7 to 3.5 percent, by weight, of nickel; at least one element selected from among 0.02 to 0.4 percent, by weight, of bismuth, 0.02 to 0.4 percent, by weight, of tellurium, and 0.02 to 0.4 percent, by weight, of selenium; and the remaining percent, by weight, of zinc, wherein the percent by weight of copper, silicon, tin, phosphorus, manganese and nickel in the copper alloy satisfy the relationship; 55xe2x89xa6Xxe2x88x923Y+aZ+bW+cV+dUxe2x89xa670, wherein X is the percent, by weight, of copper, Y is the percent, by weight, of silicon, Z is the percent, by weight, of tin, W is the percent, by weight, of phosphorus, V is the percent, by weight, of manganese, U is the percent, by weight, of nickel, a is xe2x88x920.5, b is xe2x88x923, c is 2.5, d is 2.5, and the percent by weith of silicon, manganese and nickel satisfy the relationship; 0.7xe2x89xa6Y/(V+U)xe2x89xa66; and the copper alloy has a metal construction comprising multiple phases integrated to form a composite phase, wherein the composite phase is an xcex1 phase matrix having a total phase area comprising not more than 5% of xcex2 phase, and 5-70% of the total phase area is provided by at least one phase selected from the group consisting of a xcex3 phase, a xcexa phase, and a xcexc phase. The eighth copper alloy will be hereinafter called the xe2x80x9ceighth invention alloy.xe2x80x9d
The eighth copper alloy contains at least one element selected from among 0.02 to 0.4 percent, by weight, of bismuth, 0.02 to 0.4 percent, by weight, of tellurium, and 0.02 to 0.4 percent, by weight, of selenium in addition to the components in the seventh invention alloy. While high-strength features and wear resistance as high as in the seventh invention alloy are secured, the eighth invention alloy is further improved in machinability by the addition of at least one element selected among bismuth and other elements which are effective in raising the machinability through a mechanism different from that exhibited by silicon. The reasons for adding machinability improvers such as bismuth and others and deciding on the quantities thereof to be added are the same as those given for the second, fourth, and sixth invention alloys. The grounds for adding the other elements, that is, copper, zinc, tin, manganese, and nickel, and setting the contents thereof, are the same as given for the seventh invention alloy.
A lead-free free-cutting copper alloy also with excellent machinability coupled with a good high-temperature oxidation resistance which is composed of 69 to 79 percent, by weight, of copper; 2.0 to 4.0 percent, by weight, of silicon; 0.1 to 1.5 percent, by weight, of aluminum; 0.02 to 0.25 percent, by weight, of phosphorus; and the remaining percent, by weight, of zinc, wherein the percent by weight of copper, silicon, aluminum and phosphorus in the copper alloy satisfy the relationship; 55xe2x89xa6Xxe2x88x923Y+aZ+bWxe2x89xa670, wherein X is the percent, by weight, of copper, Y is the percent, by weight, of silicon, Z is the percent, by weight, of aluminum, W is the percent, by weight, of phosphorus, a is xe2x88x922, and b is xe2x88x923; and the copper alloy has a metal construction comprising multiple phases integrated to form a composite phase, wherein the composite phase is an xcex1 phase matrix having a total phase area comprising not more than 5% of a xcex2 phase, and 5-70% of the total phase area is provided by at least one phase selected from the group consisting of a xcex3 phase, a xcexa phase, and a xcexc phase. The ninth copper alloy will be hereinafter called the xe2x80x9cninth invention alloy.xe2x80x9d
Aluminum is an element which improves the strength, machinability, wear resistance, and also high-temperature oxidation resistance. Silicon, too, has a property of enhancing the machinability, strength, wear resistance, resistance to stress corrosion cracking, and also high-temperature oxidation resistance of an alloy, as mentioned above. Aluminum works to raise the high-temperature oxidation resistance when the aluminum is added in amounts of not less than 0.1 percent by weight, together with silicon. But when increasing the addition of aluminum beyond 1.5 percent by weight, no proportional results can be expected with respect to high-temperature oxidation resistance. For this reason, the addition of aluminum is set at 0.1 to 1.5 percent by weight.
Aluminum is also effective in promoting the formation of the gamma phase. The addition of aluminum together with tin or in place of tin could further improve the machinability of the Cuxe2x80x94Sixe2x80x94Zn alloy. Aluminum is also effective in improving the strength, wear resistance, and high-temperature oxidation resistance as well as the machinability and also in minimizing the specific gravity. If the machinability is to be improved at all, aluminum will have to be added in amounts of at least 1.0 percent by weight.
Phosphorus is added to enhance the flow of molten metal in casting. Phosphorus also works to improve the aforesaid machinability, dezincification resistance, and high-temperature oxidation resistance, in addition to the flow of molten metal. Those effects are exhibited when phosphorus is added in an amount not smaller than 0.02 percent by weight. But even if phosphorus is used in an amount of more than 0.25 percent by weight, it will not result in a proportional increase in effect. For this reason, the addition of phosphorus is set at 0.02 to 0.25 percent by weight.
While silicon is added to improve the machinability of an alloy as mentioned above, it is also capable of increasing the flow of molten metal as is phosphorus. The effect of silicon in improving the flowability of molten metal is exhibited when it is added in an amount not smaller than 2.0 percent by weight. The range of the addition of silicon for improving the flowability of molten metal overlaps that for improvement of the machinability thereof. Taking both of these factors into consideration, the addition of silicon is set in the range 2.0 to 4.0 percent by weight.
A lead-free free-cutting copper alloy also with excellent machinability and good high-temperature oxidation resistance which is composed of 69 to 79 percent, by weight, of copper; 2.0 to 4.0 percent, by weight, of silicon; 0.1 to 1.5 percent, by weight, of aluminum; 0.02 to 0.25 percent, by weight, of phosphorus; at least one element selected from among 0.02 to 0.4 percent, by weight, of chromium and 0.02 to 0.4 percent, by weight, of titanium; and the remaining percent, by weight, of zinc, wherein the percent by weight of copper, silicon, aluminum, phosphorus and chromium in the copper alloy satisfy the relationship; 55xe2x89xa6Xxe2x88x923Y+aZ+bW+cVxe2x89xa670, wherein X is the percent, by weight, of copper, Y is the percent, by weight, of silicon, Z is the percent, by weight, of aluminum, W is the percent, by weight, of phosphorus, V is the percent, by weight, of chromium, a is xe2x88x922, b is xe2x88x923, c is 2; and the copper alloy has a metal construction comprising multiple phases integrated to form a composite phase, wherein the composite phase is an xcex1 phase matrix having a total phase area comprising not more than 5% of a xcex2 phase, and 5-70% of the total phase area is provided by at least one phase selected from the group consisting of a xcex3 phase, a xcexa phase, and a xcexc phase. The tenth copper alloy will be hereinafter called the xe2x80x9ctenth invention alloy.xe2x80x9d
Chromium and/or titanium are added in order to improve high-temperature oxidation resistance. Good results can be expected especially when they are added together with aluminum to produce a synergistic effect. Those effects are exhibited when the addition is 0.02 percent or more by weight, whether they are used alone or in combination. The saturation point is 0.4 percent by weight. In consideration of these observations, the tenth invention alloy contains at least one element selected from among 0.02 to 0.4 percent by weight of chromium and 0.02 to 0.4 percent by weight of titanium in addition to the components of the ninth invention alloy, and thus is an improvement over the ninth invention alloy with regard to the high- temperature oxidation resistance of the alloy produced.
A lead-free free-cutting copper alloy also with excellent machinability and a good high-temperature oxidation resistance which is composed of 69 to 79 percent, by weight, of copper; 2.0 to 4.0 percent, by weight, of silicon; 0.1 to 1.5 percent, by weight, of aluminum; 0.02 to 0.25 percent, by weight, of phosphorus; at least one element selected from among 0.02 to 0.4 percent, by weight, of bismuth, 0.02 to 0.4 percent, by weight, of tellurium, and 0.02 to 0.4 percent, by weight, of selenium; and the remaining percent, by weight, of zinc, wherein the percent by weight of copper, silicon, tin and phosphorus in the copper alloy satisfy the relationship; 55xe2x89xa6Xxe2x88x923Y+aZ+bWxe2x89xa670, wherein X is the percent, by weight, of copper, Y is the percent, by weight, of silicon, Z is the percent, by weight, of aluminum, W is the percent, by weight, of phosphorus, a is xe2x88x922, and b is xe2x88x923; and the copper alloy has a metal construction comprising multiple phases integrated to form a composite phase, wherein the composite phase is an xcex1 phase matrix having a total phase area comprising not more than 5% of a xcex2 phase, and 5-70% of the total phase area is provided by at least one phase selected from the group consisting of a xcex3 phase, a xcexa phase, and a xcexc phase. The eleventh copper alloy will be hereinafter called the xe2x80x9celeventh invention alloy.xe2x80x9d
The eleventh invention alloy contains at least one element selected from among 0.02 to 0.4 percent, by weight, of bismuth, 0.02 to 0.4 percent, by weight, of tellurium, and 0.02 to 0.4 percent, by weight, of selenium, in addition to the components of the ninth invention alloy. While having as high a high-temperature oxidation resistance as the ninth invention alloy, the eleventh invention alloy is further improved in machinability by the addition of at least one element selected from among bismuth and other elements which are effective in raising machinability through a mechanism other than that exhibited by silicon.
A lead-free free-cutting copper alloy also with excellent machinability and a good high-temperature oxidation resistance which is composed of 69 to 79 percent, by weight, of copper; 2.0 to 4.0 percent, by weight, of silicon; 0.1 to 1.5 percent, by weight, of aluminum; 0.02 to 0.25 percent, by weight, of phosphorus; at least one element selected from among 0.02 to 0.4 percent, by weight, of chromium, and 0.02 to 0.4 percent by weight of titanium; at least one element selected from among 0.02 to 0.4 percent, by weight, of bismuth, 0.02 to 0.4 percent, by weight, of tellurium, and 0.02 to 0.4 percent, by weight, of selenium; and the remaining percent, by weight, of zinc, wherein the percent by weight of copper, silicon, aluminum, phosphorus and chromium in the copper alloy satisfy the relationship; 55xe2x89xa6Xxe2x89xa63Y+aZ+bW+cVxe2x89xa670, wherein X is the percent, by weight, of copper, Y is the percent, by weight, of silicon, Z is the percent, by weight, of aluminum, W is the percent, by weight, of phosphorus, V is the percent, by weight, of chromium, a is xe2x88x922, b is xe2x88x923, c is 2; and the copper alloy has a metal construction comprising multiple phases integrated to form a composite phase, wherein the composite phase is an xcex1 phase matrix having a total phase area comprising not more than 5% of a xcex2 phase, and 5-70% of the total phase area is provided by at least one phase selected from the group consisting of a xcex3 phase, a xcexa phase, and a xcexc phase. The twelfth copper alloy will be hereinafter called the xe2x80x9ctwelfth invention alloy.xe2x80x9d
The twelfth invention alloy contains, in addition to the components of the tenth invention alloy, at least one element selected from among 0.02 to 0.4 percent, by weight, of bismuth, 0.02 to 0.4 percent, by weight, of tellurium, and 0.02 to 0.4 percent, by weight, of selenium. While as high a high-temperature oxidation resistance as in the tenth invention alloy is obtained, the twelfth invention alloy is further improved in machinability by adding at least one element selected from among bismuth and other elements which are effective in raising the machinability through a mechanism other than that exhibited by silicon.
A lead-free free-cutting copper alloy, also with further improved machinability, is obtained by subjecting any one of the preceding invention alloys to a heat treatment for 30 minutes to 5 hours at a temperature of from 400xc2x0 C. to 600xc2x0 C. This thirteenth copper alloy will be hereinafter called the xe2x80x9cthirteenth invention alloy.xe2x80x9d
The first to twelfth invention alloys contain machinability improving elements such as silicon and have an excellent machinability because of the addition of such elements. Of those invention alloys, the alloys with a high copper content which have large amounts of other phasesxe2x80x94mainly alloys having a kappa phase percentage greater than the total percentage of their alpha, beta, gamma, and delta phases togetherxe2x80x94can further improve in machinability in a heat treatment. As a result of the specified heat treatment, the kappa phase turns into a gamma phase. The gamma phase finely disperses and precipitates to further enhance the machinability of the alloy. The present alloys with high copper content are high in ductility of the matrix and low in absolute quantity of gamma phase, and therefore are excellent in cold workability. But in cases where cold working, such as caulking and cutting, are required, the aforesaid heat treatment is very useful.
In other words, among the first to twelfth invention alloys, those which are high in copper contentxe2x80x94with gamma phase in small quantities and kappa phase in large quantitiesxe2x80x94(hereinafter referred to as the xe2x80x9chigh copper content alloyxe2x80x9d) undergo a change in phase from the kappa phase to the gamma phase during the heat treatment. As a result, the gamma phase is finely dispersed and precipitated, and the machinability of the alloy is improved. In practice, during the manufacturing process of castings, expanded metals, and hot forgings, the materials are often force-air-cooled or water cooled depending on the forging conditions, productivity after hot working (hot extrusion, hot forging, etc.), working environment, and other factors. In such cases, among the first to twelfth invention alloys, those with a low content of copper (hereinafter called the xe2x80x9clow copper content alloyxe2x80x9d) are rather low in the content of the gamma phase and contain beta phase. During the heat treatment, the beta phase changes into the gamma phase, and the gamma phase is finely dispersed and precipitated, whereby the machinability is improved.
Experiments show that heat treatment is especially effective: with high copper content alloys, where the mixing ratio of copper and silicon to other added elements (except for zinc) A is given as 67xe2x89xa6Cuxe2x88x923Si+aA; and with low copper content alloys, where the mixing ratio of copper and silicon to other added elements (except for zinc) A is given as 64xe2x89xa7Cuxe2x88x923Si+aA. It is noted that xe2x80x9caxe2x80x9d is a coefficient. The coefficient is different depending on the added element A. For example, with tin, a is xe2x88x920.5; aluminum, xe2x88x922; phosphorus, xe2x88x923; antimony, 0; arsenic, 0; manganese, +2.5; and nickel, +2.5.
In accordance with the present invention, heat treatment at a temperature of less than 400xc2x0 C. is not economical and practical, because the aforesaid phase change will proceed slowly and much time will be needed to obtain satisfactory results. At temperatures over 600xc2x0 C., on the other hand, the kappa phase will grow or the beta phase will appear, bringing about no improvement in machinability. From a practical viewpoint, therefore, it is contemplated that the heat treatment be performed for 30 minutes to 5 hours at 400xc2x0 C. to 600xc2x0 C.